1. Field of the Invention
The invention relates to a radio communication apparatus and a radio communication method, which allow a plurality of radio systems to share and use a frequency band.
2. Description of the Related Art
Conventionally, a radio apparatus and method which allow a plurality of radio systems to share and use a frequency band are known. In the conventional radio apparatus and method of this type, a radio apparatus with a low priority level performs carrier detection (to be also referred to as carrier sense hereinafter) of the shared frequency band, and transmits a signal when it determines that this frequency band is not used by a radio system with a high priority level (for example, see J. Mitola III, “Cognitive Radio for Flexible Mobile Multimedia Communications,” IEEE Sixth International Workshop on Mobile Multimedia Communications (MoMuC99), pp. 3-10, November 1999.)
Also, in a conventional communication system that makes information transmission using transmission frames, a technique for sequentially transmitting at least two types of transmission frame detection symbols generated by orthogonal frequency division multiplex (OFDM) modulation using a plurality of frequency subcarriers in one transmission frame is known (for example, see JP-A 2000-188583 (KOKAI)).
The aforementioned related art is a technique that allows a receiving terminal to detect the transmission frame when the frequency channel used in radio communications is known in advance in transmitting and receiving terminals. Hence, the receiving terminal cannot detect the frequency channel which is selected by the transmitting terminal to transmit a transmission frame, and the frame itself, thus posing a problem.